The present invention relates to a method and an apparatus for utilizing a cellular network by way of an IP network.
In recent years, an attempt to connect a telephone via an Internet has been made. This attempt is generally called Voice over Internet Protocol (VoIP). The greatest advantage of the VoIP is that the inexpensive Internet can be used as a communication line for transferring voice data. As for standards of the VoIP, there are H.323 and SIP for instance, and these are laid down by ITU (International Telecommunication Union) and IETF (Internet Engineering Task Force) respectively. As for telephone terminals used therefore, a fixed telephone and a personal computer having a microphone and a speaker are presumed.
In recent years, portable telephones are also remarkably widespread. A portable telephone is generally connected to a cellular network via a base station. On the other hand, it is expected that the future portable telephone will also have a short distance communication IF such as a Bluetooth IF mounted thereon. It will be possible, by mounting the Bluetooth IF, to connect the portable telephone to the personal computer, a peripheral, a household appliance and so on via a radio channel. In particular, it will be possible, by connecting it to an access point of the Internet via the Bluetooth IF, to access the Internet from the portable telephone and not via a public network such as a cellular network. In this case, there is an advantage that the Internet can be inexpensively accessed because the expensive cellular network is not used.
Incidentally, the International Patent Publication WO00/51375 discloses an invention wherein a so-called dual mode terminal on which a communication IF for the cellular network and the short distance communication IF are mounted is used so as to utilize the cellular network and the IP network.
According to the prior art, a subscriber's number and an IP address of the portable telephone are stored on the cellular network side so as to transfer an incoming call to the portable telephone via the IP network. For that reason, it was necessary for a home location register (HLR) and a visitor location register (VLR) on the cellular network side to manage the IP address of the portable telephone or information on an IP telephone gateway to be connected to the IP network in addition to ordinary location registration information. For this purpose, it was necessary to significantly improve the HLR and VLR on the cellular network side. In general, an improvement on the cellular network side is accompanied by change in a signaling interface and so on and so it is apt to become a large-scale improvement, which is difficult to implement.
In addition, according to the prior art, it was possible to register the portable telephone only in an area in which a user thereof actually exists.